"I thought that there was nothing Donald Trump could say that would shock me, but I was wrong. I was just totally shocked at the performance of Donald Trump in Helsinki at a press conference with Vladimir Putin. I just found that it was outrageous," said Brennan to anchor Brian Williams on MSNBC immediately following Trump's press conference in Helsinki, Finland.

The commentary from Brennan, who serves as an MSNBC contributor, came after Trump and Putin met one-on-one for the first time. During the news conference that followed the two-hour meeting, Putin again denied that Russia interfered in the 2016 U.S. presidential election. Trump, meanwhile, contradicted his own intelligence agencies while saying special counsel Robert MuellerRobert Swan MuellerSasse: US should applaud choice of Mueller to lead Russia probeMORE's investigation "is a probe that has been disastrous for the country."

"I cannot understand how the national security team can continue to abide by this and how Pompeo and Bolton and Kelly can continue in their jobs," Brennan, who served under President Obama from 2013 to 2017, said.

"This, I think, rises to the point of good American patriots resigning in objection to that performance by Donald Trump. I’m at a loss of words to describe just how outrageous his words, his statements, his behavior has been ... and how Mr. Putin now is the master puppeteer of Donald Trump, the person who is in our Oval Office. Outrageous.”

Brennan took to Twitter shortly after the TV appearance to continue the sentiment, calling Trump's rhetoric "nothing short of treasonous."

Donald Trump’s press conference performance in Helsinki rises to & exceeds the threshold of “high crimes & misdemeanors.” It was nothing short of treasonous. Not only were Trump’s comments imbecilic, he is wholly in the pocket of Putin. Republican Patriots: Where are you???

Trump during the news conference did not condemn Russian meddling in the 2016 election, opting to agree with Putin, who said "the Russia state" was not involved.

“He just said it’s not Russia,” Trump said in echoing Putin’s denials of involvement in the U.S. election. “I will say this, I don’t see any reason why it would be.”

Trump also attempted to turn the focus of a question about Russian election meddling to the Democratic National Committee's server and the deleted emails from the private server 2016 Democratic nominee Hillary Clinton used while secretary of State.

“What happened to the server?” Trump asked. “What happened to the Clinton emails?”

Prominent news anchors and hosts on MSNBC rivals CNN and Fox condemned Trump in strong terms following the press conference.

CNN's Anderson Cooper, for example called the president's performance "disgraceful," while Fox's Neil Cavuto described it as “humiliatingly embarrassing, and just a joke" shortly after the press conference ended.